Collagen-based wound dressings: control of the pore structure and morphology.

Collagen-based sponges have been used as both temporary and permanent coverings for dermal defects in animals and humans. Cellular ingrowth within such a sponge has been shown to depend on the porosity and the presence of fibrous structure. Collagen sponges were made by freezing and freeze-drying dispersions under acidic conditions. These studies involved the effects of dispersion pH and viscosity as well as freezing temperature on the surface and bulk morphology of collagen-based sponges. Using scanning electron and light microscopy, the results of these studies indicated that large surface pores that form connections (channels) with the interior of the sponge were formed using low-viscosity collagen dispersions. At high dispersion pH (3.2) and at a moderate freezing temperature (-30 degrees C), fibrous structure and a large number of channels were present. When a lower dispersion pH (2.0) and freezing temperature (-80 degrees C) were used, pores sizes were smaller with channels and fibrous structure, whereas a higher freezing temperature (-20 degrees C) resulted in a sheet-like structure and increased pore sizes. Differences in pore size and surface morphology were explained on the basis of ice crystal growth. In the case of abundant free water (high pH) and high freezing temperature, the pore size was greatest because of enhanced ice crystal growth.